yes, omapi-port parameter in the config file enables OMAPI in dhcpd, well it should, or it could, and whether the fact that it does not work when no -cf/-lf are submitted is a result of intentional programming or it is a simply a bug, I cannot tell.
it would be worth asking developers themselves, to me it's obvious misbehaviour, if not, I can only ask, why?
just use omapi-port in the config, run it from prompt or with service, you should see no dhcp listening on your chosen port
run it with quick fix or from prompt with earlier mentioned params and dhcp should be fine having port opened
cheers

Hi,
sorry for such a big delay.
I tested this issue, but for me it works.
I added omapi-port to dhcpd.conf and started dhcpd without -cf and -lf.
Then on client machine I started dhclient to obtain address from server.
Then I used omshell (OMAPI Command Shell) to connect to server and
query its state via OMAPI. And I succeeded.
N-V-R: dhcp-4.1.1-22.P1.fc13.i686
In more detail:
1) on server (192.168.0.113)
$ cat /etc/dhcp/dhcpd.conf
omapi-port 520;
subnet 192.168.0.0 netmask 255.255.255.0 {
range 192.168.0.11 192.168.0.20;
}
$ dhcpd -d eth1
2) on client
$ dhclient -d eth1
bound to 192.168.0.11
$ omshell
> server 192.168.0.113
> port 520
> connect
obj: <null>
> new lease
obj: lease
> set ip-address = 192.168.0.11
obj: lease
ip-address = c0:a8:00:0b
> open
obj: lease
ip-address = c0:a8:00:0b
state = 00:00:00:02
subnet = 00:00:00:02
pool = 00:00:00:03
hardware-address = 08:00:27:9a:d0:ef
hardware-type = state = 00:00:00:01
ends = 4c:2a:b8:c6
starts = 4c:2a:10:06
tstp = 00:00:00:00
tsfp = 00:00:00:00
atsfp = 00:00:00:00
cltt = 4c:2a:10:06
flags = 00
I can see all the information the DHCP server has about that particular lease.
So the OMAPI obviously runs on server even if started without -cf and -lf.
How do you check whether the port is opened?
I used 'nmap -A localhost' on server, but there's no 520 port mentioned
regardless of whether I run the server with or without -cf/-lf.

I'm closing this as worksforme because
with 'nmap -A localhost -p 520' or 'ss -lnptu' or 'lsof -i'
I see that dhcpd listens on defined omapi-port
regardless of whether I run the server with or without -cf/-lf.